Journal of Manufacturing Processes最新文献

Electromagnetic joining technology is widely utilized in assembling tubular components due to its ability to exert uniform magnetic pressure. To augment this pressure, a field shaper structure has been introduced. However, the conventional design may impair the uniformity of deformation, particularly at the seam. This study presents a novel multi-layer field shaper (MLFS) to enhance deformation uniformity. The performance of the MLFS was evaluated and optimized through experimental trials and simulation analysis. The results showed that MLFS achieved a 300 % increase in minimum deformation with a 56 % reduction in the aspect ratio, demonstrating that our design effectively balances efficiency with deformation uniformity. The magnetic cubic decay formula could fit the simulation data well with R² higher than 0.999. MLFS was found to enhance uniformity by creating a more even magnetic field that decreased the curvature near the plastic hinge. Compared to altering the interlayer thickness, adjusting the interlayer angle can further enhance uniformity. When the rotation angle is 60°, the radius range can be further reduced by 32.5 %, 39.0 %, and 12.2 % at energy levels of 27 kJ, 30 kJ, and 33 kJ, respectively. The above results indicate that by designing and optimizing MLFS, sufficiently large and uniform electromagnetic forces were obtained.

To improve the bending and interlayer properties of hybrid-fiber-reinforced composites (HFRCs), a functionally graded hybrid (FGH) strategy is proposed inspired by the graded structure of bamboo. Specimens were prepared by utilizing the continuous-fiber 3D-printing manufacturing process, achieving graded changes in the fiber content and properties of the composites between and within layers. The differences in the mechanical properties and failure mechanisms of traditional interlayer HFRCs (IHFRCs) and functionally graded HFRCs (FGHFRCs) were comparatively analyzed. The mechanical-property test results demonstrated that the FGH strategy can further improve the mechanical properties of HFRCs. Compared with those of the IHFRCs, the bending strength and interlayer shear strength of the FGHFRCs increased by a maximum of 25.95 % and 41.20 %, respectively. Macro-micro fracture morphology analysis revealed that the interlayer hybrid led to a risk of delamination failure. However, the FGH effectively reduced the interlayer performance differences, changed the direction of crack propagation along the interlayer, and effectively suppressed the generation of delamination damage, which was conducive to further improving the properties of HFRCs. Owing to their enhanced properties and positive hybrid effect, the manufacturing process and the FGH strategy have considerable potential in engineering applications.

Although the simulation results had demonstrated that the strain field introduced by Ni₄Ti₃ nano-precipitates in NiTi shape memory alloys (SMAs) was related with their superelasticity inherently, the corresponding experimental result was rarely documented heretofore, especially in additive manufactured NiTi SMAs. In this work, we tailor the morphologies and resultant strain field of Ni₄Ti₃ nano-precipitates by heat treatment of a NiTi SMA subjected to laser powder bed fusion (LPBF), and further authenticate relationship between the superelasticity and the strain field in the LPBF NiTi samples. When holding times were 1 h, 3 h, and 5 h at aging temperature of 350 °C after solution treatment, the Ni₄Ti₃ nano-precipitates in the LPBF NiTi samples exhibit spherical, ellipsoidal, and lenticular morphologies, respectively. Accordingly, the strain field around Ni₄Ti₃ nano-precipitates in B2 matrix decrease from 0.15 % to 0.13 % and 0.10 %, respectively. The LPBF and aged NiTi samples present large superelasticity, which exceeds 6 % recovery strain together with high recovery rate of ˃99 % during 10-times cyclic compression loading. Interestingly, the LPBF and aged sample with the spherical Ni₄Ti₃ and highest strain field displays the worst superelasticity stability, while the one with the lenticular Ni₄Ti₃ and smallest strain field exhibits the relatively stable and biggest superelasticity of 6.36 %. Basically, this is attributed to different mechanisms between the Ni₄Ti₃ nano-precipitates and dislocations generated during cyclic loading, which is induced by different interfaces between the Ni₄Ti₃ and B2 matrix in the three types of the NiTi samples. For the sample with the highest strain field, its spherical Ni₄Ti₃ was cut through by generated dislocations due to coherent interface between the spherical Ni₄Ti₃ and B2 matrix. In contrast, the one with the smallest strain field, its lenticular Ni₄Ti₃ can impede effectively generated dislocations because of semi-coherent or non-coherent interface between the lenticular Ni₄Ti₃ and B2 matrix. Therefore, these results can provide meaningful insights into tailoring the nano-precipitates and thereby obtaining excellent superelasticity of NiTi SMAs by LPBF.

Laser vision based real-time welding seam tracking has emerged as a potent strategy for enabling intelligent robotic welding. And trackers based seam key point tracking algorithms demonstrate remarkable adaptability to complex welding environments. This paper proposed a self-supervised robust KCF (Kernelized Correlation Filter) tracker for seam key point tracking, which could be a novel approach to achieve autonomous seam tracking. Firstly, a self-supervised global-local feature extraction network is constructed, which can guide the model to focus on both global semantic and local texture features of laser stripes, thereby establishing a solid groundwork for stable key point tracking. Subsequently, a robust KCF tracking algorithm is presented. A multi-template enhanced tracker generation strategy is designed, and the corresponding analytical solution is derived, which can improve the tracker's representation capability of stripe features without significantly increasing computational complexity. Experimental results demonstrate that compared to traditional algorithms, the proposed algorithm exhibits advantages in tracking accuracy, stability, and real-time performance. Moreover, since the algorithm minimally relies on manually labeled data, it holds promise as a technological means to achieve fully autonomous seam tracking in actual welding production.

Binder jetting additive manufacturing (AM) has emerged as a promising technique for mass-producing items, especially when using metallic materials that are challenging to fabricate in alternative AM processes such as laser powder bed fusion (LPBF). The binder jetting process has the advantage of not involving melting and solidification, which makes it a potential solution for materials such as NiTi shape memory alloys. This approach offers key benefits, including enhanced reliability and isotropic material properties. Recent studies of these alloys in LPBF, while generating promising results, have highlighted the significant costs and technical challenges. This paper presents the first investigation of binder jetting of NiTi, addressing critical aspects of materials and processing, including powder characteristics, binder properties, and process parameters. More specifically, this study explores detailed analyses of powder properties, binder characteristics determined through thermogravimetric analysis (TGA), and the optimization of binder saturation levels. The curing, debinding, and sintering processes were examined in terms of furnace conditions, atmospheres, and temperatures to ensure precise control over the final material properties. Findings from elemental analysis during debinding and a comprehensive evaluation of sintered NiTi components, including density measurements, optical microscopy, backscattered electron (BSE) imaging, elemental analysis, and differential scanning calorimetry (DSC), are presented. These insights are essential for optimizing the mechanical and structural characteristics of the manufactured NiTi alloy components. The results of this paper will be crucial in the optimization of critical parameters to produce high-quality NiTi components with tailored mechanical and thermal properties, opening new horizons for their applications across diverse industries.

Selective laser melting (SLM) offers advanced solutions for manufacturing high added value titanium alloy (Ti-alloy) components, owing to its capability to facilitate rapid, integrated, and customisable manufacturing of complex parts. However, surface machining is imperative for SLM-manufactured (SLM-ed) components due to the poor surface integrity. SLM-ed Ti-alloy is a typical difficult-to-machine material, conventional machining methods are difficult to realize high-efficiency and high-quality machining of SLM-ed Ti-alloy. Ultra-high-speed machining (UHSM) exhibits immense potential for enhancing machining efficiency and quality. However, the material removal mechanism of SLM-ed Ti-alloy in ultra-high-speed regions remains unclear. This study develops a single-point scratching (SPS) system to investigate material removal mechanisms across speeds ranging from 20 m/s to 220 m/s. Systematic characterisations regarding surface creation, subsurface microstructure, and chip formation were conducted using FIB and STEM techniques. The results revealed that the pile-up effect was significantly suppressed at higher speeds. The machining-deformed zone (MDZ) exhibited a “skin effect,” with plastic deformation confined to a superficial layer with a depth within 1 μm at 220 m/s. The deformation mechanism transitioned from dislocation-mediated deformation (DMD) to twin-mediated deformation (TMD) under extremely high strain rate conditions, leading to the formation of ultrafine grains with embedded twins (UGENTs) structure. Additionally, the chip removal mode progressively shift from continuous chips to segmented chips, and eventually to fragmented chips with increased scratching speed. This study provides an insight into the material removal and deformation process of SLM-ed Ti-alloy under low to ultra-high-speed deformations, and lays the theoretical basis for the high-efficiency and high-quality machining of difficult-to-machining materials.

In the manufacturing process, chatter detection is essential to preserving product quality, minimising tool wear, and ensuring efficient productivity. Conventional chatter detection methods often lack the precision required to accurately capture chatter frequencies, which motivates research into advanced signal processing approaches. This paper proposes a wavelet-Hilbert technique (WHT) to get over this limitation of the conventional method. The integration of wavelet synchrosqueezing transform (WSST) and Hilbert-Huang transform (HHT) methods strengthens the robustness of chatter detection algorithms, allowing them to perform effectively across a range of machining conditions. It employs a synchrosqueezing process that increases the time frequency localization, providing the signal component with a clearer representation and increasing detection accuracy. Its integrating nature, which enables comprehensive analysis and effective chatter detection, makes it a novel approach. The force and acceleration signals were used in a comparative test. The comparison analysis demonstrates that signals with lower computing complexity (acceleration signals) are more appropriate. Subsequently, further testing and the collection of acceleration signals were carried out to fully validate the proposed method. The Renyi entropy's value was ascertained. The proposed method offers a higher-resolution TFR and an average Renyi entropy value of 12.3 in comparison to the conventional method's fuzzy representation and entropy value of 15.1.

In this study, a novel method for predicting microstructure evolution through secondary post-processing of finite element method (FEM) simulation results is proposed. This developed method integrates grinding process variables (strain ε, strain rate $\dot{\epsilon }$, temperature T, stress σ, etc.) with the unified constitutive equations of Inconel 718 to calculate the distribution of normalized dislocation density $\overline{\rho }$, recrystallization volume fraction S, and grain size d at any frame time. Furthermore, the microstructure evolution during ultrasonic vibration-assisted grinding (UVAG) was analyzed under varying ultrasonic vibrations A, spindle speeds n, and grinding depths a_p. The research results indicate that the microstructure evolution mainly divided into three stages, resulting in the formation of refined grain region and high-density dislocation region in the ground surface layer. Ultrasonic vibration increases the depth of the refined grain region and the dislocation density in the ground surface layer, due to the strain increases and temperature decreases caused by periodic vibration. Additionally, increases in spindle speed and grinding depth leads to higher dislocation density, recrystallization fraction, and refine grain depth. The microstructures (dislocation density, depth of refine grain region) in the ground surface layer were characterized via transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD), and the experimental results verified the effectiveness of the developed method for predicting microstructure evolution. This method provides a new approach for understanding and controlling the microstructure evolution of the grinding surface of Inconel 718 during the UVAG process.

State-of-the-art laser beam-powder bed fusion (PBF-LB) metal additive manufacturing (AM) systems are capable of producing dense workpieces without systematically occurring defects. Nonetheless, stochastically occurring defects with significant impacts on material quality levels persist. One possible cause is the fallout effects of spatter, matter ejected from the process zone, which may redistribute back onto the powder bed. The understanding of spatter redistribution and its impact on the PBF-LB process is still developing. This work provides insight on the nature and causes of spatter redistribution through a study of process variables and responses. Additionally, fundamental gaps in process-monitoring technology are addressed through a multi-modal sensing approach to spatter measurement. High-resolution optical layer-wise imaging was utilized to capture spatter concentration over the powder bed as a function of carrier gas flow direction, spatter generating workpiece location, distance from said workpiece, gas flow condition, and laser scan direction. These data were compared to ultra-high spatial resolution optical imaging as well as topographical measurements of the powder bed, which served to benchmark data and quantitatively capture powder bed quality measures. Spatter particles themselves were also characterized and correlated to powder bed location. It was concluded that even nominal carrier gas flow conditions fail to evacuate large spatter particles, which may be up to five times as large as feedstock powder. Additionally, the vast majority of large spatter particles tended to redistribute within 0–10 mm of the spatter generating workpiece. This observation contradicts commonplace assumptions that spatter may travel the full distance of the powder bed before landing on a workpiece. It also suggests that workpieces self-contaminate with spatter, this possibly being a significant contributor to lack-of-fusion porosity formation.

A new oscillation-loaded dynamic micro embossing (DME) process was developed as an efficient and flexible deformation-based method to manufacture micro structures on both planar and curved surfaces. This unique process utilizes current to stimulate miniature punch fixed to a small electrodynamic vibrator to oscillate and thus periodically emboss part surface, contributing to the advantages of high efficiency, low forming force and high flexibility. However, the geometry and morphology of micro structure formed by DME process is difficult to control and tailor due to the deficient understanding of the electro-mechanical coupled forming process. Therefore, experimental investigations and theoretical modelling were conducted to unravel the process mechanics and the quantitative relationship between structure geometry and process parameters. Employing punch with single rectangular strip feature, micro grooves and cubic pillars with different widths were obtained on the pure copper workpieces of different grain sizes. The geometry of the formed micro structure was found to be slightly asymmetrical as the result of the kinetic and mechanical interaction between punch and workpiece during forming process. In addition, the quality of formed micro structures was significantly influenced by both the punch feature size and material grain size. The reduction of punch feature size or the rise of grain size can aggravate surface roughening morphology and thus the dimension scatter of formed micro structures. Based on the energy conversion mechanics during the DME process, an analytical structure geometry model to predict the structure geometric dimensions with different process parameters was established and validated via corroboration with experimental results. Furthermore, the influence of process parameters on the structure depth formability was thoroughly revealed. The structure depth formability first surges with the current frequency and then declines when the current frequency exceeds the resonant frequency, and can be significantly improved by elevating the current amplitude.